Instron AVE2 - Chapter 4: Mark Specimens; Overview

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Chapter 4
Mark specimens
• Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
• Marking tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
• Applying ink dots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
• Troubleshooting ink dots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Overview
The most common method of marking uses white or black ink dots. Marking jigs for
various gauge lengths are provided with the extensometer. White and black marking
pens are also provided.
When deciding how to mark your specimens, you must consider:
• the mark material - inks and tape dots both contain solvents that may affect the
strength of the specimen
• the mark color - the color of the mark must contrast with the color of the specimen
as seen by the camera, which uses polarized light
• in most cases, white marks produce the best results, even on specimens that
appear white to the human eye
• white marks produce the best results on reflective metal specimens and dark
color plastic specimens
• if white causes problems, the best alternative is black, provided it contrasts
sufficiently with the specimen background color, as seen by the camera, which
uses polarized light
• for most applications, you should not use silver marks as these appear black to
the camera, although they may be effective on white specimens if white marks
cause problems
• the shape and size of the mark must be compatible with the profile of the specimen